With fins:
If you eliminate the heat exchanger alltogether then fins will improve heat transfer IN THE DIRECTION OF HIGHER TEMP TO LOWER TEMP. I don't know the temperature of an engine bay nor the temp of the heated intake charge from the turbo so I can't really say..
anyways, another thing you could try is having a multiple tubes with water flowing through them inside the intake tube. That'll get you more surface area..
Sorry for insisting so much but I still think that cooling air with the fuel already mixed in is not such a good idea.. I would seriously look into water injection. I started looking at info about it and was seriously surprised. And it seems to me that it is way easier to setup than any intercooler setup. In my opinion the only drawback to water injection is that you seriously have to check the water level..
Again, sorry for being so insistive..
Luis
